This
slide and slide 28 illustrate the diversity
of size and morphology of the volcano-tectonic structures known as coronae.
A typical corona consists of an inner circular plateau; a ridged, raised
rim; and an annular trough. Volcanic features in the interior are common.
The median diameter for coronae is ~250 kilometers, and the diameters
of over two-thirds of the coronae are within 150 kilometers of the median.

This slide shows
two of the largest coronae, Heng-O (2°N, 355°E) and Ceres (16°S,
151.5°E).